A computationally efficient method for improving the speed of full wave analysis CAD programs for microstrip circuits

Approximations to the Green´s functions used in full wave microstrip circuit analysis programs are presented. The approximations have a number of advantages. They rely on the substrate of the circuit being electrically thin, which is reasonable assumption in realistic circuits. There is no restriction on lateral separation between two points. If the substrate is thin enough, the approximation presented can be used instead of calculating the Green´s functions numerically. If the substrate is thicker, the form of the approximation can still be used; the coefficients are determined numerically at a few points by numerical evaluation of the Green´s functions. Another advantage of this representation is that it can be used to speed up the run time of the matrix fill when several frequencies are needed. This results in substantial savings of time in the computer-aided design program.<>